Such a pressure control module is discussed for example in DE 40 30 980 A1. The two-channel pressure control module has a respective channel for a brake actuator of a right-hand wheel and a brake actuator for a left-hand wheel on an axle and contains, per channel, an electropneumatic valve unit which controls a relay valve and which has in each case one inlet valve and one outlet valve and also a backup valve.
In undisrupted operation, i.e. with the electrics and voltage supply intact, depending on a driver's request, an electric brake request signal is input into a control device which outputs control commands for the inlet valve or outlet valve, in order to ventilate or vent a control chamber of the associated relay valve. In the process, a pressure sensor connected to the control chamber of the relay valve measures the working pressure generated in a working chamber of the relay valve and sends a corresponding signal to the control device, in order to realize pressure control for the respective channel. In undisrupted operation, i.e. with the electrics intact, the backup valves are in the blocking position, i.e. a pneumatic brake request signal generated in parallel with the electric brake request signal is not transmitted to the control chambers of the relay valves. The pneumatic brake request signal and the electric brake request signal are generated by a foot brake module.
If the voltage supply fails or there is a fault in the electrics, the control device is deenergized and the backup valves switch under spring loading into their passage position, such that the pneumatic brake request signal switches as control pressure onto the control chambers of the relay valves, which thereupon generate an uncontrolled working pressure as braking pressure in their working chambers.
For separate control of the braking pressure in the two channels, the working chambers of the relay valves are connected to in each case one pressure sensor, such that a separate pressure sensor is available per channel and separate control of the two channels of the pressure control module is realized. However, as a result, the structure of such a pressure control module is relatively complex.